Various researches have been made to use substances such as carbon dioxide, water and propane in a supercritical state. Among these, U.S. Pat. No. 4,820,752 discloses, when blending additives into polymer materials such as rubbers or plastic materials to introduce additives to a polymer material, without using mechanical mixing means, by dissolving the additives in a compressed fluid of a substance normally (i.e., at an ordinary temperature and an ordinary pressure) in a gaseous state and bringing the fluid into contact with the polymer material. Further, JP-A-8-169979 discloses a method for treating and recycling vulcanized fluoro rubber waste by a mixture of a supercritical fluid and a strong alkali aqueous solution.
Further, JP-A-11-348037 discloses a method of modification by impregnating an antioxidant, antisticking agent, wax, etc. into a vulcanized rubber shaped article by supercritical state carbon dioxide in which these are dissolved. However, none of these documents discloses the concept of newly introducing a cross-linkable or polymerizable monomer, oligomer, or polymer into a cross-linked elastomer composition, followed by polymerizing or cross-linking to thereafter form the formation of a new polymer network in an existing polymer network.
Further, Journal of Supercritical Fluids 17 (2000) 65-72 describes modification of a polymer by supercritical impregnation, but there is not deemed to be any description in this publication regarding modification of a cross-linked polymer.